The inventors have proposed a crown gear deceleration mechanism that has a constitution shown in FIG. 25 as a deceleration mechanism capable of realizing high reduction ratio and low backlash, although it is a simple structure.
As disclosed also in JP 4511635 B2, this crown gear deceleration mechanism includes a stator 102 and a rotor 104. The stator 102 is a crown gear that is fixed to an external member. The rotor 104 is another crown gear that is different from the stator 102. Then, the rotor 104 is pressed to a side of the stator 102 with a pressing mechanism 106 operated so as to rotate around an axis. The rotor 104is engaged with the stator 102. In this case, both of teeth of the rotor 104 and teeth of the stator 102 have been set so that the rotor 104 inclines slightly to the stator 102 and engagement parts are distributed to two places existing at both sides between which a devotion center line intervenes. The rotor 104 is coupled to an output shaft 112 through flexible spokes 108 and a hub 110.
In the crown gear deceleration mechanism that includes the above-mentioned configuration, the pressing mechanism 106 is rotated with power of a motor or the like. Therefore, the rotor 104 performs a precession while moving, in a circumferential direction, the parts where the rotor 104 is engaged with the stator 102. Rotation is transmitted to the output shaft 112 from the rotor 104 while each spoke 108 deforms elastically in connection with this precession. Therefore, the rotation input into the pressing mechanism 106 is outputted at high reduction ratio through the output shaft 112. Further, according to the crown gear deceleration mechanism, because the teeth are constantly engaged with each other at each of the two places of both sides, the low backrush is realized.
Furthermore, in a crown gear deceleration mechanism disclosed in JP 5054853 B2, an elastic disc is provided between a rotor and an output shaft, and then the rotor is coupled to the output shaft. In this crown gear deceleration mechanism, when the rotor performs a precession, the elastic disk transmits rotation to the output shaft while elastically deforming.